1. Field of the Invention
This invention relates to an apparatus for supplying materials, employed when materials, particularly those having high heat sensitivity material such as foods, chemicals, etc., are supplied onto a belt continuously moving inside a vacuum dryer and dried.
2. Description of the Prior Art
In order to prevent materials as mentioned above from denaturation by heat, it has been thought of to lower the vaporization temperature of the water contained therein, and thus a vacuum drying process has been employed.
Such a process has been usually carried out by passing a belt through a vacuum dryer. A degree of vacuum in the range of 1 to 100 Torr has been employed although it varies depending on the materials.
As what is to be particularly stressed in this case, the state of the materials distributed on the belt is mentioned. Namely, materials should be supplied onto the belt continuously, in a definite amount and in a uniform thickness. If this supplying state fluctuates, the balance between the materials and the heat quantity supplied is destroyed, resulting in heat denaturation of the materials or inferior dried products having an uneven water content.
Accordingly, in order to continuously obtain dried products of good quality under optimal conditions and in a short time, it is necessary to supply materials under optimal conditions depending on the physical properties of the materials. Thus it has been desired to provide an apparatus for supplying materials which makes it possible to realize supplying conditions depending on the respective physical properties of different materials and yet makes easy the operation or control therefor.
Now, as for apparatuses currently employed as those of such a kind, apparatuses as shown in FIG. 1, FIG. 2 and FIG. 3 of the accompanying drawings may be illustrated.
The apparatus shown in FIG. 1 is referred to generally as the slit type supplying apparatus, wherein a supplying apparatus 1 is provided above a belt 3 tensioned on a roller 2 which, in turn, is provided inside a vacuum drying chamber (not shown).
In this supplying apparatus 1 a material "a" is supplied through ducts provided outside the drying chamber and equipped with a stop valve 5 and flow control valves 4, to a distributing chamber 6, by means of a metering pump (not shown), and is distributed onto the belt 3 through a distributing nozzle 7 provided in front of and at the lower end of the distributing chamber. In addition, a cooling chamber 10 is provided adjacent to the distributing chamber 6, and cooling water is introduced into the cooling chamber through an inlet tube 8 and discharged therefrom through an outlet tube 9.
The apparatus shown in FIG. 2 is referred to generally as a pipe type supplying apparatus 1 wherein a material "a" is distributed onto a belt 1 through ducts equipped with a stop valve 5 and control valves 4 in the same manner as in FIG. 1, and further through a plurality of supply tubes 11 arranged in parallel to the moving direction of the belt and on the same level as that of the belt surface.
The apparatus shown in FIG. 3 is referred to generally as an orifice type supplying apparatus 1, wherein a material "a" is supplied into a plurality of distributing chambers 14 provided above a belt (not shown), through ducts equipped with a stop valve 5 and control valves 4 in the same manner as in FIG. 1 and FIG. 2, and further supplied onto the belt through distributing nozzles 13 bored in a bottom plate 12.
However, each of the above-mentioned conventional apparatuses has the following drawbacks:
(1) In the apparatuses of FIG. 1, FIG. 2 and FIG. 3, the control of the amount supplied and the stopping of the supply may be carried out at the outlet of nozzle 7 (FIG. 1), nozzle 13 (FIG. 3) or supply tubes 11 (FIG. 2), but this requires a complicated mechanism; hence they have been employed operating valves 4 and stop valve 5 provided outside the drying chamber.
However, between the control valves 4 and stop valve 5 and the outlet 7, 11 or 13, are located ducts, the distributing chamber, etc., and due to the effect of the preceding material present therein, a time-lag occurs between the time of operation of the control valves 4 and stop valve 5 and the time at which the material leaving the outlet 7, 13 or 11 is actually controlled in amount or stopped. As for this time-lag, the higher the concentration or the viscous property of the material, the longer is the time-lag, which makes difficult the correct control or stopping.
(2) Further, in the apparatuses of FIG. 1, FIG. 2 and FIG. 3, as for the material present between the control valves 4 and the stop valve 5 and the outlet 7, 11 or 13, even when the control valves 4 and the stop valve 5 are closed at the time of stopping the material supply, the material flows out of the outlet onto the belt, little by little over a long time, under the influence of the negative pressure inside the drying chamber. The material which has flowed out becomes an excessively dried product and mixes in the normally dried product to reduce the quality of the product. Thus, in order to prevent this, even if the belt motion is stopped at the same time as the stopping of the material supply, the flowing-out of the material onto the belt cannot be prevented, and removal of this material which has flowed out and a washing operation therefor become necessary.
(3) Particularly in the apparatus of FIG. 1, when the nozzle 7 has a uniform width, the velocity of the material "a" on the belt 3 is distributed so that the velocity may be higher at the central portion thereof and lower on both the sides thereof, as shown in FIG. 4A.
Such a difference in the velocity distribution results, as it is, in a difference in the amount of the material distributed on the belt. Thus, in order to make the distribution uniform, it has been attempted, for example, to provide a core which constitutes a body resistant to flow, in front of a nearly central portion of the nozzle 7. As a result, the velocity distribution is improved as shown in FIG. 4B. However, the shape, location, etc. of such a core must be adequately selected depending on the physical properties of the material, hence such an operation is very difficult.
Thus, as a method for avoiding such a difficulty, increase in the number of ducts to the distributing chamber 6, variance in the aperture width of the nozzle, or the like means may be thought of, but the design or manufacture of such a means is also difficult.
(4) For the above-mentioned reasons, it has been impossible for any of conventional apparatuses to carry out an increase or decrease in the supply amount and stop the supply in a short time and correctly, and hence it has been very difficult for them to yield a material having a moisture content in a definite amount and continuously.